Solectek skyway series, Руководство пользователя

Страница: 224 / 262

198
Basic Concepts
Radio Signals
To visualize radio (RF) waves, consider the waves created when an object moves in
water. Water waves are strongest near their source, but they decrease in size as they
spread in all directions.
Radio waves fan out from their source in a similar manner. They travel best in empty
space, but they can also pass through gasses, such as air, and many other substances.
The lower the frequency of an RF signal, the more substances it can penetrate. The
ability of a directional antenna to focus radio waves is analogous to a magnifying glass
focusing sunlight into a very concentrated hot spot.
A directional antenna focuses the waves in one direction. It forms them into a conical
shape that makes them stronger and enables them to travel greater distances.
In the same way that light is focused by a magnifying glass, an RF signal shaped by an
antenna is strongest within a narrow area at the center of the cone. We call this area
the center lobe. For optimum long-distance reception, an antenna must be aligned to
receive the center lobe signal, and the signal path must be free of obstructions.
The signal forms a cone as
it leaves the antenna.